DE102015201460B4 - Position determination of a medical instrument - Google Patents

Abstract

Method for determining the position of a medical instrument (4), at least one light-sensitive sensor (1) with at least two sensor elements (2) being arranged on the medical instrument (4), on which light (L) is incident at an angle of incidence (α, α ₁ , α ₂ , α ₃ , α ₄ ), which is emitted by at least one light source (5) arranged at a known position, and a measured variable dependent on the angle of incidence (α, α ₁ , α ₂ , α ₃ , α ₄ ) for determining the position and/or the orientation of the medical instrument (4) is detected using radiation intensities acting on the sensor elements (2), the sensor surfaces (3) assigned to the sensor elements (2) being arranged at a predetermined angle to one another.

Description

The invention relates to a method and a device for determining the position of a medical instrument.

Various methods and devices for determining the position of medical instruments, in particular in connection with active or passive surgical navigation, are known from the prior art. For example, to determine the position and/or the orientation of the medical instrument, imaging methods are used that enable real-time localization and thus active guidance of the medical instrument. In other medical applications, the medical instrument is mechanically coupled to a moveable support arm. In these cases, the position of the medical instrument can be determined by detecting the deflection or the position of the carrier arm.

From the disclosure document DE 198 25 221 A1 a method for position determination is known, in which the radiation emitted by point sources is detected by so-called angle-measuring optical, stationary sensors. The disclosure document DE 11 2011 103 016 T5 describes optical sensors which have several sensor elements arranged in one plane to detect the angle of incidence of light. From the disclosure document WO 2008/119 766 A1 an ambient light sensor is known which is designed to detect a global light intensity.

Proceeding from this prior art, it is the object of the present invention to specify an improved method for determining the position of a medical instrument, which can be implemented particularly easily.

With regard to the method, the object is achieved by a method of the type mentioned at the beginning with the further features of patent claim 1.

Advantageous configurations of the invention are the subject matter of the dependent claims.

In a method for determining the position of a medical instrument, at least one light-sensitive sensor with at least two sensor elements is arranged on the medical instrument, onto which light falls at an angle of incidence, which is emitted by at least one light source arranged at a known position. To determine the position and/or the orientation of the medical instrument, a measured variable dependent on the angle of incidence is recorded using radiation intensities acting on the sensor elements, with the sensor surfaces assigned to the sensor elements being arranged at a predetermined angle to one another.

The invention makes use of technological developments in the field of sensor technology in order to specify a reliable system for position determination, which enables precise determination of the position or orientation of the medical instrument, for example as part of surgical navigation. Sensors with a sufficiently good resolution for precise detection of the angle of incidence have compact designs whose sizes are in the range of approximately 1 mm ² , for example. The handling or guidance of the medical instrument is therefore at most insignificantly impaired by the at least one sensor arranged there. According to the invention, the position and/or the orientation of the medical instrument is determined at least partially based on the determined angle of incidence with respect to the at least one light source. The method according to the invention can therefore be implemented using particularly simple means.

In particular, pointers that point to medical structures come into consideration as medical instruments. Other exemplary embodiments include instruments for laparoscopic surgery, in particular laparoscopes, radiofrequency and cryoablation devices.

In order to adequately determine the orientation and/or the position, depending on the specific application, a number of light sources placed at different predetermined and known positions in space and a number of sensors can be provided on the medical instrument. In possible exemplary embodiments of the invention, the movement of the medical instrument is limited to a few degrees of freedom, for example by means of mechanical holding elements or carrier arms, so that only a reduced number of light sources and/or sensors is required to enable complete position determination. In the case of a medical instrument restricted to linear translation, for example, it is sufficient to provide a light source and a sensor, since in this case the position of the medical instrument is already completely determined by detecting the angle of incidence relative to the known position of the light source. In the case of a substantially free movement of the medical instrument in three-dimensional space, at least a partial position determination is possible by detecting the incident angle on the at least one sensor and from the at least one light source emitted light possible.

The measured variable preferably includes a current intensity of an electrical current that is at least partially caused by the photoelectric effect or an electrical resistance modified by the photoelectric effect. In particular, the sensor can have photodiodes or photoresistors switched in the flow direction or in the blocking direction for detecting such measured variables. In another exemplary embodiment, CCD sensors and/or photon-counting detectors are used, which are designed to supply a measured variable that is dependent on the incident light intensity.

In one possible exemplary embodiment of the invention, the at least one light source emits light with at least one frequency from the infrared frequency range. Accordingly, the sensor designed to detect the emitted light is designed as an infrared sensor, with which the angle of incidence can be correctly determined.

In another exemplary embodiment, the at least one light source emits light with at least one frequency from the optically visible frequency range. In other words, a conventional light source is used here to determine the position or orientation of the medical instrument. The at least one sensor is then designed accordingly as an optical sensor.

In a particularly preferred embodiment, a plurality of light sources are provided, which are arranged in space at different known positions. The light sources emit light with slightly different characteristic frequency distributions; in particular, in a specific exemplary embodiment, the individual light sources can emit light with frequencies from mutually non-overlapping frequency ranges. The light source corresponding to the origin of the incident light can then be selected on the sensor side, for example by means of a suitable filter. In any case, the light sources emit light with frequency distributions that differ from one another in pairs, so that the origin of the light incident on the at least one sensor can be assigned by means of frequency selection on the sensor side. Such designs have the advantage that the number of sensors on the medical instrument required for determining the position can be reduced, since the frequency selection on the sensor side makes it possible to determine the relative position of the sensor with respect to different light sources. A negative impact on the handling of the medical instrument by the sensors fitted there can therefore be further reduced.

With regard to the device, the object is achieved by a device for determining the position of the medical instrument of the type mentioned at the beginning with the further features of patent claim 6.

According to the invention, the device is designed to carry out the method described above, so that reference is first made to the previous statements.

The device for determining the position of the medical instrument comprises the at least one light source, which is arranged at a known position in space, and the at least one light-sensitive sensor, which is attached to the medical instrument. The at least one sensor comprises at least two light-sensitive sensor elements whose sensor surfaces are arranged at a predetermined angle to one another. The light source can in particular be spatially separate or attached to a medical device, in particular to an X-ray device having a C-arm. The at least one light source emits light which is incident on the sensor at the angle of incidence. The at least one sensor is designed to detect a measurement variable that is dependent on the angle of incidence. The angle of incidence can be determined from the measured variable in order to determine the position and/or orientation of the medical instrument.

According to the invention, the at least one sensor comprises at least two light-sensitive sensor elements, for example photodiodes or photoresistors, which are arranged at a predetermined angle to one another, in particular orthogonally to one another. The angle of incidence can be determined from measured variables that depend on the intensity of the light incident on the respective sensor element, taking the geometry into account. Such measured variables are, for example, the strength of a photocurrent or the amount of an illumination-dependent resistance. In other embodiments, photon counting detectors or CCD sensors are provided.

In order to determine the position and the orientation of the medical instrument in three-dimensional space, the at least one sensor comprises four sensor elements in a preferred exemplary embodiment, the sensor surfaces of which are arranged in pairs at a predetermined angle, in particular pairs orthogonally to one another.

In another preferred exemplary embodiment, the at least one sensor for determining the angle of incidence is provided with three spaced-apart light-sensitive sensor elements whose sensor surfaces are arranged at an angle to one another or in one plane.

Flat designs are preferred in particular in cases in which the largest possible measuring range is to be recorded, since in principle they enable the entire half-space located above the plane to be recorded. To detect the half-space, the sensor surfaces of the three light-sensitive sensor elements run flat in the plane, with the three light-sensitive sensor elements preferably being arranged at an angle of 120° to one another.

Sensors with planar arrays of sensor elements are optimized to ensure the largest possible coverage of the measuring range. Depending on the medical application, however, it can happen that the intensity of the light incident on the individual sensor elements differs only slightly and as a result the angle of incidence derived therefrom is associated with a relatively large degree of inaccuracy. Another exemplary embodiment that is optimized in terms of measurement accuracy includes a sensor with at least three light-sensitive sensor elements that are spaced apart from one another and are arranged on a common conical surface. Since the sensor surfaces of the sensor elements are now arranged at an angle to one another, which i.a. depends on the opening angle of the cone surface or of the cone, the dependence of the intensities impinging on the respective sensor elements on the angle of incidence is increased. Accordingly, the angle of incidence can be determined more precisely with such arrangements.

It goes without saying that the size of the measurement range and the measurement accuracy are in an inverse relationship (trade-off). The measuring range is at its maximum in a planar arrangement that corresponds to an opening angle of 180°. The more acute the opening angle of the cone surface, the greater the measuring accuracy and the smaller the measuring range. In particularly preferred exemplary embodiments, the opening angle of the conical surface is between 60° and 80°.

According to alternative exemplary embodiments, particularly in the case of sensors whose sensor elements are arranged on conical surfaces, provision is made for the inwardly directed sensor surfaces to be curved or planar. In the case of sensors that have sensor elements with flat sensor surfaces, these are preferably arranged in such a way that their central longitudinal axes run on the conical surface.

At least two light-sensitive sensors are preferably arranged at a predetermined distance on the medical instrument. The position and orientation of the medical instrument in the plane defined by the at least one light source and the at least two sensors can then be determined from the given distance and the at least two angles of incidence detected by the respective sensors.

In a development of the invention, three spaced-apart light-sensitive sensors are provided on the medical instrument in an arrangement that deviates from a collinear configuration. Such designs enable the unambiguous determination of the position of medical instruments that can move freely in space.

Four sensors, which are arranged in pairs of sensors, are particularly preferably provided for determining the position of the medical instrument. Each pair of sensors is provided in a linear array, with a first pair of sensors being arranged in an orthogonal configuration with respect to a second pair of sensors.

A plurality of light sources are preferably arranged at different known positions, which emit light with pairs of different frequency distributions. The at least one sensor has means for frequency selection, such as corresponding filters, so that the light source corresponding to the origin of the light incident on the at least one sensor can be assigned by the sensor. The frequency selection on the sensor side enables the position of the at least one sensor to be determined with respect to angles of incidence that correspond to the positions of the various light sources. The number of sensors provided on the medical instrument can thus be reduced, since a sensor designed in this way enables several independent parameters suitable for position determination to be recorded.

The light-sensitive sensors for detecting the angle of incidence are preferably provided on the medical instrument and the light sources are arranged at known positions in space. However, it goes without saying that a correspondingly inverted arrangement, in which the light sources and the sensors are swapped in terms of their spatial arrangement, is also suitable for determining the position of the medical instrument. For the sake of simplicity, exemplary embodiments with a certain number of light sources and sensors are specifically described, in which the sensors are always provided on the medical instrument and the light sources in the room. The corresponding inverted version includes corresponding devices in which the light sources are arranged on the instrument side and the sensors are arranged at the known positions in space.

• 1 ein Sensor zur Erfassung eines Einfallswinkels in einer Schnittdarstellung;
• 2 eine Vorrichtung zur Positionsbestimmung, umfassend eine Lichtquelle und ein medizinischen Instrument mit zwei Sensoren in einer schematischen Darstellung;
• 3 ein medizinisches Instrument mit zwei Sensorpaaren in einer orthogonalen Konfiguration in einer schematischen Draufsicht,
• 4 eine weitere Vorrichtung zur Positionsbestimmung, bei der der Sensor Mittel zur Frequenzselektion aufweist und mehrere Lichtquellen vorgesehen sind, die Licht unterschiedlicher Frequenzen emittieren,
• 5 ein plan ausgeführter Sensor zur Erfassung des Einfallswinkels im dreidimensionalem Raum in einer Draufsicht,
• 6 ein weiterer Sensor zur Erfassung des Einfallswinkels im dreidimensionalen Raum, dessen Sensorelemente auf einer Kegelfläche angeordnet sind, in einer perspektivischen Darstellung.

For a further description of the invention, reference is made to the exemplary embodiments of the drawings. It shows in a schematic principle sketch:

• 1 a sensor for detecting an incident angle in a sectional view;
• 2 a device for position determination, comprising a light source and a medical instrument with two sensors in a schematic representation;
• 3 a medical instrument with two pairs of sensors in an orthogonal configuration in a schematic plan view,
• 4 a further device for position determination, in which the sensor has means for frequency selection and several light sources are provided which emit light of different frequencies,
• 5 a planar sensor for detecting the angle of incidence in three-dimensional space in a plan view,
• 6 another sensor for detecting the angle of incidence in three-dimensional space, the sensor elements of which are arranged on a cone surface, in a perspective view.

Corresponding parts are provided with the same reference symbols in all figures.

1 FIG. 12 schematically illustrates a sensor 1 designed to detect the angle of incidence α, which includes two photodiodes 2 whose sensor surfaces 3 are directed in the direction of the normal N to the surface. The photodiodes 2 are arranged at an angle β, which is 45° in the example shown. Correspondingly, the two sensor surfaces 3 are arranged orthogonally to one another here.

If light L strikes the sensor 1 in the direction of the angle of incidence α, the photodiodes generate electrical currents whose current strengths depend on the radiation intensity acting on the respective photodiode 2 . The angle of incidence α of the incident light L can therefore be determined from the ratio of the two current intensities.

In another exemplary embodiment, an illumination-dependent resistance can be recorded as a measured variable to determine the angle of incidence α.

by means of the in 1 sensor 1 shown, the angle of incidence α can be completely determined in the plane shown.

In another possible exemplary embodiment, sensors 1 that include four photodiodes 2 are provided for the complete determination of angles of incidence α in three-dimensional space. Each two of the photodiodes 2 are to each other, as in 1 shown, arranged. A first pair of photodiodes 2 extends in the in 1 shown plane of the drawing, a further, second pair of photodiodes 2 is arranged perpendicular to the plane of the drawing shown.

2 1 shows a medical instrument 4 to which two sensors 1 are fastened, which are designed to detect measurement variables dependent on angles of incidence α ₁ , α ₂ . A light source 5 is placed at a known position in space. Without restricting the generality, the center of the light source 5 can serve as the origin for a fixed coordinate system whose first axis X and second axis Y are shown.

The light source 1 emits light L, which impinges on the respective sensors 1 at the angle of incidence α ₁ , α ₂ . The position and the orientation of the medical instrument 4 in the plane shown can be clearly determined from the measured angles of incidence α ₁ , α ₂ and the known distance Δz of the two sensors 1 relative to one another. In other words, the coordinate transformation from the stationary coordinate system to the instrument-fixed coordinate system in the plane is determined by the values for the angles of incidence α ₁ , α ₂ and the distance Δz. The first axis X' and the second axis Y' of the instrument-fixed coordinate system are in 2 shown.

3 shows schematically a medical instrument 4, which is equipped with four sensors 1 for determining the corresponding coordinate transformation in three-dimensional space. The sensors 1 of a first sensor pair 6 are arranged at a distance Δz from one another. Correspondingly, the sensors 1 of a further, second pair of sensors 7 are arranged at a distance Δz′ from one another. The first and the second pair of sensors 6, 7 assume an orthogonal configuration to one another, so that the position and the orientation of the medical instrument 4 depend on the angles of incidence α ₁ , α ₂ , α ₃ , α ₄ that can be detected by the sensors 1 and the distances Δz , Δz' are completely determined.

4 FIG. 12 shows a further exemplary embodiment of the invention in a schematic representation, in which the sensor 1 additionally has a filter 8 which enables a frequency selection of the light L detected. In this exemplary embodiment, the device for determining position comprises two light sources 5 which are arranged at different but known locations in space. The two light sources 5 emit light in the visible range with slightly different frequencies. The filter 8 can be used to select frequencies in such a way that only light emitted by one of the two light sources 5 is detected. Correspondingly, the angle of incidence α ₁ with respect to a first light source 9 and the angle of incidence α ₂ with respect to a second light source 10 can be determined with the sensor 1 shown.

5 shows another embodiment of the sensor 1 in a top view. The sensor 1 is flat and comprises three sensor elements 3, the sensor surfaces 3 of which run in the plane of the drawing. The individual sensor elements 3 are arranged at an angle γ to one another, which is 120° in the example shown.

Such a sensor 1 is designed to detect the entire half-space located above the plane of the drawing.

6 shows another sensor 1 for detecting the angle of incidence α in three-dimensional space in a perspective view. The sensor 1 has three sensor elements 2 which are arranged on a conical surface 11 at regular intervals from one another. The sensor surfaces 3 of the sensor elements 2 are directed inwards.

In such an arrangement, the intensity of the incident light L detected by the respective sensor elements 2 is highly dependent on the angle of incidence α. The angle of incidence α can therefore be recorded particularly precisely with such a sensor 1 .

An opening angle δ of the conical surface 11 determines the relative orientation of the sensor surfaces 3 to one another, which is approximately 65° in the example shown. With respect to a further surface 12 defining the surface of the sensor 1, the sensor elements 2 are arranged at an angle γ to one another, which is approximately 120° in the example shown.

It goes without saying that in particular the 5 and 6 shown embodiments are designed to detect the complete solid angle α, from which the light L is incident on the sensor 1, and not just an angle with respect to a given preferred direction. The figures were shown in a highly schematic manner in this respect only for reasons of better representation.

In a method for determining the position of the medical instrument 4 , the measurement variable that is dependent on the angle of incidence α is recorded using at least one light-sensitive sensor 1 provided on the medical instrument 4 . In order to at least partially determine the position and/or the orientation of the medical instrument 4, the angle of incidence α is derived from the measured value. According to various application examples, a plurality of sensors 1 or a plurality of light sources 5 can optionally be provided in order to ensure that the position and/or orientation of the medical instrument 4 is adequately determined.

Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Reference List

1

sensor

2

sensor element

3

sensor surface

4

instrument

5

light source

6

First pair of sensors

7

Second pair of sensors

8th

filter

9

First light source

10

Second light source

11

conical surface

12

Surface

L

Light

α, α1, α2, α3, a4

angle of incidence

β, γ

angle

δ

opening angle

Δz, Δz'

Distance

X, X'

First axis

Y, Y'

second axis

Claims (14)

Method for determining the position of a medical instrument (4), at least one light-sensitive sensor (1) with at least two sensor elements (2) being arranged on the medical instrument (4), on which light (L) is incident at an angle of incidence (α, α ₁ , α ₂ , α ₃ , α ₄ ), which is emitted by at least one light source (5) arranged at a known position, and a measured variable dependent on the angle of incidence (α, α ₁ , α ₂ , α ₃ , α ₄ ) for determining the position and/or the orientation of the medical instrument (4) is detected using radiation intensities acting on the sensor elements (2), the sensor surfaces (3) assigned to the sensor elements (2) being arranged at a predetermined angle to one another. procedure after claim 1 , wherein the measured variable comprises a current strength of an electrical current caused at least partially by the photoelectric effect or an electrical resistance modified by the photoelectric effect. procedure after claim 1 or 2 , wherein the at least one light source (5) emits light (L) with at least one frequency from the infrared frequency range. Method according to one of the preceding claims, wherein the at least one light source (5) emits light (L) with at least one frequency from the optically visible frequency range. Method according to one of the preceding claims, wherein a plurality of light sources (5, 9, 10) arranged at different known positions emit light (L) with frequency distributions which are different from one another in pairs and an assignment of the origin of the light incident on the at least one sensor (1) ( L) based on the emitted frequency distribution by means of a sensor-side frequency selection. Device for determining the position of a medical instrument (4), which is designed to determine the position and/or the orientation of the medical instrument (4) according to one of the preceding claims, at least one light-sensitive sensor (1) being arranged on the medical instrument (4). , on which light (L) is incident at an angle of incidence (α, α ₁ , α ₂ , α ₃ , α ₄ ), which can be emitted by at least one light source (5) arranged at a known position and by which at least one sensor (1st ) a measured variable dependent on the angle of incidence (α, α ₁ , α ₂ , α ₃ , α ₄ ) for determining the position and/or the orientation of the medical instrument (4) can be detected, with the at least one sensor (1) having at least two light-sensitive sensors Includes sensor elements (2) whose sensor surfaces (3) are arranged at a predetermined angle to one another. device after claim 6 , wherein the at least two light-sensitive sensor surfaces (3) are arranged orthogonally to one another. device after claim 6 or 7 , wherein the at least one sensor (1) comprises four light-sensitive sensor elements (2), the sensor surfaces (3) of which are arranged in pairs at a predetermined angle, in particular pairs orthogonally to one another. device after claim 6 or 7 , wherein the at least one sensor (1) comprises at least three spaced-apart light-sensitive sensor elements (2) with sensor surfaces (3). device after claim 9 , wherein the sensor elements (2) are arranged on a conical surface. device after claim 10 , the conical surface having an included angle (δ) of 60° to 80°. Device according to one of Claims 6 until 11 , At least two light-sensitive sensors (1) being arranged at a predetermined distance (Δz, Δz') on the medical instrument (4). Device according to one of Claims 6 until 12 At least three light-sensitive sensors (1) spaced apart from one another are provided on the medical instrument (4) in an arrangement that deviates from a collinear configuration. Device according to one of Claims 6 until 13 , wherein a plurality of light sources (5, 9, 10) are arranged at different known positions, which emit light (L) with pairs of different frequency distributions and the at least one sensor (1) has means for frequency selection, so that the origin of the on the light source (5, 9, 10) corresponding to the at least one sensor (1) incident light (L) can be assigned.

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